1. Field of the Invention
This invention relates to a non-aqueous ink-jet ink composition for use in a printer for recording information. This invention particularly relates to a non-aqueous ink-jet ink composition containing a non-volatile solvent as a principal constituent.
2. Description of the Related Art
Ink jet recording techniques enable low-noise, quick printing to be performed and have rapidly become popular in recent years. With ink jet printers, liquid ink compositions having a high fluidity are jetted out from fine nozzles, and information is thereby recorded on recording paper. The ink jet printers may be roughly classified into on-demand jetting-out types and continuous jetting-out types.
The ink compositions for use in the ink jet recording techniques may be roughly classified into aqueous types of ink compositions and non-aqueous types of ink compositions. Ordinarily, the aqueous types of the ink compositions contain water-soluble dyes, such as acid dyes, direct dyes, or basic dyes, which have been dissolved in a glycol type of solvent and water. However, ordinarily, the problems are encountered in that recorded matter obtained with the ink jet recording techniques, in which the aqueous types of the ink compositions are employed, have a low water resistance.
The non-aqueous types of the ink compositions have the advantages in that the non-aqueous types of the ink compositions are capable of yielding recorded matter having a high water resistance. The non-aqueous types of the ink compositions may be classified into solvent types of ink compositions, which contain volatile solvents as principal constituents, and oil types of ink compositions, which contain non-volatile solvents as principal constituents. In particular, with the oil types of the ink compositions, nozzle clogging is not apt to occur, and a frequency of a cleaning operation during the printing operation is capable of being kept low. Therefore, the oil types of the ink compositions are appropriated for use in quick ink jet printers, and a wide variety of kinds of ink compositions have heretofore been proposed as the oil types of the ink compositions.
A high storage stability is required of the ink compositions, such as the aqueous types of the ink compositions and the non-aqueous types of the ink compositions. If the storage stability of the ink compositions is insufficient, the ink jetting-out operation will become unstable. As a result, problems with regard to a lack of an image region in the formed image, blotting of the formed image, or insufficiency in image density (particularly, occurrence of a solid image region) will occur.
As an aqueous ink composition having a storage stability and a jetting-out stability, an ink composition, which contains an inorganic sulfate for rendering a polyvalent metal soluble in water, has been proposed in, for example, Japanese Unexamined Patent Publication No. 8(1996)-337747. In cases where an anion of a carboxylic acid, or the like, which originates from an additive, or the like, undergoes coordination with a metal ion contained in a member and forms a complex having a low solubility, the problems occur in that the solubility of the metal ion becomes low, and the ink jetting-out performance becomes bad. The proposed aqueous ink composition aims at suppressing the occurrence of the problems described above with an effect of a sulfate ion having a high degree of dissociation, which sulfate ion captures the metal ion, and thereby keeping good jetting-out stability.
A non-aqueous ink composition having the storage stability has been proposed in, for example, Japanese Unexamined Patent Publication No. 2003-261808. The proposed non-aqueous ink composition contains a dispersing agent, which has an ester structure, and an ink solvent, an at least 60% by weight portion of the ink solvent being constituted of a polar organic solvent, an at least 10% by weight portion of the polar organic solvent being constituted of an ester type of solvent. Through the setting of the proportion of the polar organic solvent to be at least 60% by weight with respect to the total solvent, and through the specific selection of the ester type of the solvent and the dispersing agent having the ester structure, which solvent and the dispersing agent have good compatibility, the proposed non-aqueous ink composition aims at improving the solubility of the dispersing agent in the ink composition and suppressing pigment aggregation.
However, even though the solubility of the dispersing agent is stabilized, and the pigment aggregation is suppressed, the problems are encountered with the non-aqueous ink compositions in that sediments, such as a pigment precipitate, a gel-like foreign substance, and a rod-like crystal, occur due to a change with the passage of time. If the sediments occur, clogging of a nozzle and an ink supplying path will occur, and the ink jetting-out stability will become bad. As one of factors for the occurrence of the sediments, formation of a salt by the solvent, which has been oxidized with the passage of time, and a typical metallic element ion may be mentioned.
The typical metallic element ion originates from pigments, pigment derivatives, impurities contained at the time of pigment synthesis, a vessel, and an ink path (a tube). In particular, in the cases of the non-aqueous ink compositions, since water is not present in the system, the typical metallic element ion separates out more readily than in the cases of the aqueous ink compositions. Also, after the typical metallic element ion has separated out, the typical metallic element ion having separated out is not capable of being easily rendered soluble again. However, the technique described in, for example, Japanese Unexamined Patent Publication No. 8(1996)-337747, for capturing the metal ion having dissolved is not capable of being employed for the non-aqueous ink compositions, in which water for dissolving the ion having captured the metal ion is not present.
Therefore, as techniques for suppressing the occurrence of the sediments in the non-aqueous ink compositions, various techniques described below have heretofore been employed. For example, with one technique, the amount of a pigment treating agent is set to be large such that the typical metallic element ion may not be liberated from the pigments. With a different technique, pigments having been highly purified are utilized. With a further different technique, solvents, with which little dissolution of the typical metallic element ion from the vessel or the ink path occurs, are utilized. With another technique, in expectation of the occurrence of the sediments, the structure of the vessel for accommodating the ink composition is set such that a last portion of the ink composition is left unused for the recording operation.
However, with the technique for limiting the kinds of the pigments used or with the technique for utilizing the pigments having been highly purified, the cost of the raw materials is not capable of being kept low, and the cost of the non-aqueous ink compositions is not capable of being kept low. With the technique for utilizing the solvents, with which little dissolution of the typical metallic element ion from the vessel or the ink path occurs, the kinds of the solvents capable of being utilized are limited. Also, even though the solvents, with which little dissolution of the typical metallic element ion from the vessel or the ink path occurs, are utilized, the dissolution of the typical metallic element ion due to a change with the passage of time is not capable of being prevented from occurring. With the technique for setting the structure of the vessel for accommodating the ink composition such that the last portion of the ink composition is left unused for the recording operation, operations for recovering and scrapping the residual ink composition are required, and the use of the vessel having the specific structure causes the cost to become high.